Collapsible mandrel for forming a cavity in solid propellant rocket fuel



March 1, 1966 H H. SELLERS 3,237,913

COLLAPSIBLE MANDREL] FOR FORMING A CAVITY IN SOLID PROPELLANT ROCKET FUEL Filed June 24, 1965 4 Sheets-Sheet 1 Homer H. Sellers INVENTOR.

- ATTORNEY March 1, 1966 H H. SELLERS 3,237,913

GOLLAPSIBLE MANDREI; FOR FORMING A CAVITY IN SOLID PROPELLANT ROCKET FUEL Filed June 24, 1963 4 Sheets-Sheet 2 Homer H. Sellers INVENTOR.

' ATTORNEY 3,237,913 LID 4 Sheets-Sheet 5 Homer H. Sellers INVENTOR.

H. SELLERS FOR FORMING A CAVITY IN SO March 1, 1966 COLLAPSIBLE MANDREL PROPELLANT ROCKET FUEL Filed June 24, 1963 March 1, 1966 H. H. SELLERS 3,237,913

COLLAPSIBLE MANDREL FOR FORMING A CAVITY IN SOLID PROPELLANT ROCKET FUEL Filed June 24, 1963 4 Sheets-Sheet 4.

Fig.5

Homer H. Sellers INVENTOR.

' ATTORNEY United States Patent 3,237,913 COLLAPSIBLE MANDREL FOR FORMING A CAVITY IN SOLID PROPELLANT ROCKET FUEL Homer H. Sellers, Brunswick, Ga., assignor to Thiolrol Chemical Corporation, Bristol, Pa., a corporation of Delaware Filed June 24, 1963, Ser. No. 289,848 4 Claims. (Cl. 249-185) This invention relates to collapsible mandrels and, more particularly to a collapsible mandrel that is adapted for use in forming the cavity configuration in the solid propellant which is cast in large propulsion systems.

As the need for larger propulsion systems has arisen, it has become evident that the weight of the mandrel will necessarily increase in proportion to the size of the propulsion system. Thus, it becomes necessary to provide a mandrel that, by reason of its specific structure, will be lighter in weight than a solid mandrel, so that such a mandrel can be easily removed after the propellant has cured without damage to the cavity configuration in the propellant.

If, for example, a motor of approximately feet in diameter is to be cast, the mandrel required to form the cavity configuration would have approximately 300,000 square inches of surface area. To remove a mandrel of the size required to form the cavity in the propellant when the mandrel has to be removed as a unit, the total force essential for the removal of the mandrel could approach 500,000 to 600,000 pounds. The force of removal being based on past performances that indicate a force of 2 pounds per square inch of surface area is essential for such removal. If, due to local adhesion of the propellant to the mandrel, the amount of force set forth above was localized in one section of the motor case or if the amount of force was applied against the aft end of the motor case, disastrous results would occur. It became necessary, therefore, to create a mandrel that could be removed in sections so that the total removal force for any one section would not exceed 60,000 pounds.

An alternate method of removal of the mandrel to eliminate the use of such removal force was to provide sections that could be disassembled into relatively small parts that could be easily removed with only the lifting force necessary for the removal of each part after the disassembly of the sections into their component parts.

It is an object of this invention, therefore, to provide a mandrel that is composed of several sections with each section being susceptible of being disassembled into several parts, the removal of which from the motor case would only require lifting force and not removal force.

Such a mandrel could be easily assembled under controlled conditions, disassembled as found to be necessary, and easily shipped to any location for reassembly and reuse on repeated occasions. There are, no doubt, many conceivable structures that may be used to provide such a mandrel; and the present embodiment of the invention is, therefore, only illustrative of one approach that may be used to achieve a construction that will eliminate the difiiculty of removing, by removal force alone, a mandrel from the cured propellant.

Another object of this invention is, therefore, to provide a collapsible mandrel that may be assembled and "ice disassembled as required for use at any location when it is desired to cast a solid propellant configuration in a motor case.

With the above and other objects and advantages in view, the invention consists of the novel details of construction, arrangement and combination of parts more fully hereinafter described, claimed and illustrated in the accompanying drawings in which:

FIGURE 1 is an end view of a collapsible mandrel embodying the invention with certain parts removed or broken away to more clearly illustrate the manner of constructing an embodiment of the present invention.

FIGURE 2 is an enlarged, detailed, fragmentary View of one of the latch bolts in unlatched position.

FIGURE 3 is an enlarged transverse cross-sectional view of the mandrel taken along the line 33 of FIG- URE 1.

FIGURE 4 is also an enlarged transverse cross-sectional view taken along the line 4-4 of FIGURE 1, and

FIGURE 5 is a medial transverse cross-sectional view, with parts broken away, that is taken approximately along the line 5-5 of FIGURE 1, but shows a slightly modified form of the invention.

Referring more in detail to the drawings wherein like parts are designated by like reference numerals, the reference numeral 10 is used to designate the collapsible mandrel, embodying the invention.

The mandrel 10 consists of a plurality of similarly constructed sections; and since each section is of similar configuration to each other, it is believed that the description of one will apply to all of the sections required to fabricate a mandrel of the desired size.

It is also to be understood that the sections could vary in number and be fabricated in various sizes in order to meet the dimensional requirements of the motor case in which the propellant is to be cast.

For purposes of illustration, the mandrel 10 is of the standard six point star configuration and has outer star points 11 to 16 inclusive and inner star points 17 to 22 inclusive.

The mandrel 10 is fabricated from a plurality of sections 23 that are arranged in superposed relation to each other as shown in FIGURE 4. A centering mast 24 of cylindrical formation is used to properly align the sections 23 thereon to provide the mandrel 10. The portions of the sections 23 that extend between the outer star points and the inner star points are composed of a pair of approximately L-shaped reversely-positioned wall segments 25 and 26 respectively. The end of each of the segments 25 and 26 defining the outer star point is provided with a hinge leaf 27 through which a detachable pintle pin 28 extends, whereby the ends of the segments 25 and 26 are hingedly connected at the medial point of each of the outer star points. Positioned in contact with the inner surface of, and extending longitudinally of each of the wall segments 25 and 26, is a Wedge-shaped member 29. Arranged between and in contact with the apex portions of the wedge-shaped members 29 is another wedge-shaped member 30. The wedge-shaped members 29 and 30 are removable and are formed from a rigid or semi-rigid synthetic foam material.

Detachably mounted on the centering mast 24 is a spacer ring 31. The spacer ring 31 being in contact with the base portions of the wedge shaped members 30 to E) retain the same in position, as shown in FIGURE 1. The cooperative action of the wedge-shaped members 29 and 30 retain themselves in fixed positions, as shown in FIG- URE 1. Thus, when the wedge-shaped members 29 and 30 are in position, the mating edges 32 of the segments 25 and 26 are retained in cooperative contact with the mating edges 32 of subsequently positioned segments 25 and 26.

The opposite peripheral edges of the segments 25 and 26 are cutaway to provide ship lap joints 33 and 34 with an upper cover 35 and a lower cover 36. The lower cover 36 is provided with a concavity 37 which is adapted to receive a convexity 38 on the upper cover 35 so that a flush mating surface is provided between the sections 23 as they are placed one upon the other. An O-ring 39 positioned in a groove 40 in the convexity 38 of the upper cover 35 provides a seal between the mating surfaces of the sections 23.

Each of the covers 35 and 36 is provided with an elongated slot 41 which is in aligned relation to each other, as shown in FIGURE 4. A circular recess 42 with a diameter equal to the length of the slot 41 is provided in the outer surface of each of the covers 35 and 36, as shown in FIGURES 1 and 4. A concave recess 43 extending at right angles to the slot 41 through the medial portion thereof is provided at the bottom of the circular recess 42, as shown in FIGURES 1 and 4.

A coil spring 44 with hook formations 45 at opposite ends is extended through a tubular spring housing 46. The hook formations 45 engage the eyes 47 of the latch bolts 48 placing the spring 44 under slight tension.

To retain the covers 35 and 36 of each of the sections 23 in fixed relation to each other, the latch bolts 48 are extended through the elongated slots 41 in each of the covers 35 and 36 and rotated to align with the concave recesses 43 in the covers 35 and 36. Thus the springs 44 are under enough tension to retain the covers 35 and 36 in assembled relation to each other. The latch bolts 48 may be made from tubular stock, thus providing a means of gripping the latch bolts 48 when necessary for assembly or disassambly. In FIGURE 1, the latch bolts 48 are aligned with the concave recesses 43 with the exception of the latch bolt 48 shown in the star point that has the top cover 35 removed. This particular latch bolt 48 is in engagement with the upper edge of the spring housing 46 and has been rotated to a position where it is in alignment with the elongated slot 41 in the bottom cover 36. In FIGURE 4, the latch bolts 48 are aligned with the concave recesses 43; and thus, the sections 23 are in assembled positions to be moved as single units.

In FIGURE 5, a somewhat modified version of the invention is shown, and wherein the mandrel is designated by the reference numeral 50. The mandrel 50 is based primarily on the form of construction previously described, but is of a somewhat simplified construction. Fabrication of the mandrel 50 is also accomplished by a plurality of sections 51 that are also adapted to be arranged in superposed relation to each other. A centering mast 52 of cylindrical formation is used to align the sections 51. In this version of the invention, the wall segments 53 and 54 are constructed as previously described, but the wedge-shaped members and spacer rings are not used. The peripheral edges of the segments 53 and 54 are not machined as previously described, and the lower and upper covers 55 and 56 are cut away as at 57 to receive the peripheral edges of the segments 53 and 54, as shown in FIGURE 5. The lower cover 55 is provided with a concavity 58 which is adapted to receive a convexity 59 on the upper cover 56 so that a fiush mating surface is provided between the sections 51 as they are placed one upon the other. An O-ring 60 positioned in a groove 61 in the convexity 59 of the upper cover 56 provides a seal between the mating surfaces of the sections 51.

Each of the covers 55 and 56 is provided with an elongated slot 62, a circular recess 63 and a concave 4 recess 64 as previously described. These are in aligned relation to each other, as shown in FIGURE 5.

This version of the invention also uses the coil spring 65 with hook formations 66 at opposite ends extended through a tubular spring housing 67. The hook formations 66 engage the eyes 68 of the latch bolts 69 placing the spring 65 under slight tension.

The covers 55 and 56 of each of the sections 51 are retained in fixed relation to each other in the same manner as previously described. In FIGURE 5, the latch bolts 69 are aligned with the concave recesses 64; and thus the sections 51 are in assembled positions to be moved as a single unit. Since the wedge-shaped members and spacer rings are not used in this version of the invention, the inner ends of the covers 55 and 56 are concave, as at 70, to conform to the configurations of the centering mast 52.

In the use of both versions of the invention, the motor case is fixed in a vertical position. After the liner has been applied to the motor case, a centering mast is inserted into the aft end of the motor case. The inner end of the centering mast is extended through an opening in the head end of the motor case and secured in place. The extent to which either version of the invention can be assembled outside of the motor case depends upon the size of the opening in the aft end of the motor case, or the size of the nozzle throat opening if the nozzle is attached to the motor case prior to loading the motor.

After the propellant has been cured, the mandrel may be removed. This is accomplished by disassembling the sections and star points as they were assembled, and the various parts removed from the cavity formed by the mandrel. The centering mast is then removed, and the motor is ready for further processing.

The mandrels constructed as set forth are made from a light durable material so that such mandrels may be repeatedly used as deemed necessary, and it is believed that the manner of construction and operation of both forms of the invention will be understood by those skilled in the art.

It is also pointed out that changes in the minor details of construction, arrangement, and the combination of the associated parts may be resorted to, provided they fall Within the spirit of the invention and the scope of the appended claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A collapsible mandrel for forming the cavity configuration in the solid propellant for large propulsion units comprising a plurality of dismountable sections, a centering body positioned at the central axis of said sections to maintain said sections in longitudinal alignment within said units during the casting and curing of said solid propellant, said collapsible mandrel containing at least two star points, each of said star points including similar wall sections, upper and lower covers coacting with the peripheral edges of said sections to provide a unitary structure, each of said upper covers having a peripheral convexity thereon, each of said lower covers having a pcripheral concavity thereon that is adapted to coact with the peripheral convexity on the upper cover that is positioned in mating relation thereto, spring-biased latch means connected to and extending between said upper and lower covers of each section to maintain said upper and lower covers and said wall sections in rigid assembled relation to each other, said wall sections comprising a plurality of pairs of reversely positioned L shaped hinge leaves, pintles extending through said hinge leaves to maintain said wall sections in pivotal relation to each other, wedge-shaped members extending longitudinally of and positioned between the free ends of the hinge leaves of said wall sections in contact with the inner surface thereof to maintain said wall sections in operational relation to each other, and a spacer ring detachably mounted on said centering body and positioned in contact with the base portions of said wedge-shaped members to retain said wedge-shaped members within said wall sections.

2. A collapsible mandrel, as in claim 1, wherein tubular housings are provided for said spring-biased latch means.

3. A collapsible mandrel, as in claim 1, wherein each of said spring-biased latch means comprise a coil spring having hooked ends and latch bolts having eyes thereon for engagement with the hooked ends of said spring,

4. A collapsible mandrel, as in claim 1, wherein each of said upper and lower covers is provided with an elongated slot to permit the end of said spring-biased latch means to extend therethrough and a concavity at right angles to said slot to receive and retain therein the end of said spring-biased latch means.

References Cited by the Examiner UNITED STATES PATENTS 6 3/ 1918 McTaggart. 4/1935 Leggat et al -128 8/1939 Cobi 25- 128 4/1943 McCall 25-128 8/1951 Osborn. 1/1958 Blasius et al 25-128 8/1958 Knibb 18-45 3/1960 McGinnis et al 25-128 9/1960 Miles -356 2/196'1 Johnson et al 18-45 9/196-1 Thibodaux et al 60-356 FOREIGN PATENTS 1 1/ 193 3 Netherlands. 6/ 1954 Netherlands. 2/1957 France. 5/ 1925 Germany.

12/ 1926 Switzerland.

20 J. SPENCER OVERHOLSER, Primary Examiner.

WILLIAM J. STEPHENSON, Examiner. 

1. A COLLAPSIBLE MANDREL FOR FORMING THE CAVITY CONFIGURATION IN A SOLID PROPELLANT FOR LARGE PROPULSION UNITS COMPRISING A PLURALITY OF DISMOUNTABLE SECTIONS, A CENTERING BODY POSITIONED AT THE CENTRAL AXIS OF SAID SECTIONS TO MAINTAIN SAID SECTIONS IN LONGITUDINAL ALIGNMENT WITHIN SAID UNITS DURING THE CASTING AND CURING OF SAID SOLID PROPELLANT, SAID COLLAPSIBLE MANDREL CONTAINING AT LEAST TWO STAR POINTS, EACH OF SAID STAR POINTS INCLUDING SIMILAR WALL SECTIONS, UPPER AND LOWER COVERS COACTING WITH THE PERIPHERAL EDGES OF SAID SECTIONS TO PROVIDE A UNITARY STRUCTURE, EACH OF SAID UPPER COVERS HAVING A PERIPHERAL CONVEXITY THEREON, EACH OF SAID LOWER COVERS HAVING A PERIPHERAL CONCAVITY THEREON THAT IS ADAPTED TO COACT WITH THE PERIPHERAL CONVEXITY ON THE UPPER COVER THAT IS POSITIONED IN MATING RELATION THERETO, SPRING-BIASED LATCH MEANS CONNECTED TO AND EXTENDING BETWEEN SAID UPPER AND LOWER COVERS OF EACH SECTION TO MAINTAIN SAID UPPER 